1. Field of the Invention
The present invention relates to golf balls. More particularly, the present invention relates to golf balls having a core and a cover.
2. Description of the Related Art
A golf ball hit by a golf club flies through the air and finally falls. During the flight, the golf ball gradually slows down. Great concern of the golfers about the golf balls is their travel distance. Golfers have desired golf balls which are excellent in flight performances. As the speed immediately after impact of the golf ball (initial speed) is greater, the travel distance tends to be longer. Manufactures of the golf ball have made efforts for a long period of time to develop golf balls having high initial speed, however, initial speed which exceeds the currently provided ones is not expected. Such absence of expectation results from the regulation of upper limit of the initial speed of the golf ball defined by United States Golf Association (USGA), and thus initial speed of the golf balls purchased from major manufactures almost attains to this upper limit.
USGA also defines the lower limit of the diameter of a golf ball as 42.67 mm under its rule. In accordance with this rule, only the lower limit of the diameter is defined, but the upper limit is not defined. In other words, a large diameter of a golf ball never makes a ground for judgment of unconformity of the golf ball to the rule. However, the diameter of golf balls which are commercially available is set to be as small as possible in the range to be not less than 42.67 mm because golf balls with a small diameter have small air resistance leading to less deceleration during the flight accordingly. The diameter of all golf balls currently on the market from major manufactures is controlled in the range of from 42.67 mm to 42.80 mm.
In Japanese Patent Publication Reference JP-A-347177/1992, a golf ball having a larger diameter than usual golf balls is disclosed. Because this golf ball is hard to embed into the grass when it is placed on the fairway, it can be hit with ease. According to this golf ball, reduction of the air resistance is contemplated through ingeniously arranging dimples thereby suppressing reduction of the travel distance resulting from the large diameter.
In Japanese Patent Publication Reference JP-A Nos. 11423/1994 and 211301/1998, a golf ball having the elevated moment of inertia is disclosed through making the diameter larger. According to this golf ball, decrease of the travel distance which results from the large diameter is suppressed on behalf of the high moment of inertia.
In Japanese Patent Publication Reference JP-A-515394/2001, a golf ball having a larger diameter, with the specific gravity of the cover or the mantle layer being great is disclosed.
An object of the present invention is to further improve the flight performance of a golf ball having a large diameter. In other words, an object of the present invention is to provide a golf ball which is excellent in both terms of the easiness upon hitting and travel distance.